Here's another photo.

Looks like Birch Sawfly Caterpillars.....they can be controlled using insecticidal soap that contains Pyrethrum

Here is a link that might be useful: Birch Sawfly Caterpillars

deleted duplicate post

This post was edited by ians_gardener on Fri, Sep 6, 13 at 7:10

Sawflies are quite sensitive to plain insecticidal soap, which would be a less harsh treatment than with the added pesticide. Use a commercial insecticidal soap, rather than a home brewed concoction.

(The pyrethins, pyrethrums, pyrethroids are hazardous to a wide variety of non-target animals like beneficial insects, birds, reptiles, amphibians, and warm blooded critters like us.)

Insecticidal soap will kill young sawflies, but will not control older larva, thus the addition of pyrethins is necessary....
Pyrethins is extracted from Chrysanthemums and so is a natural organic pesticide for insects.....breaks down rapidly and so will not affect other insects.
It can be a problem for cats and fish, but caution can avoid poisoning.....

Here is a link that might be useful: Pyrethrin

You are mistaken, Ian. It DOES affect other insects....anything that it might come into contact with. And the addition of the insecticidal soap is strongly synergistic.

I'm not saying not to use it, but we all need to be fully informed about the chemicals...'organic ' or not....that we use.

I totally agree with you except that if you hit most insects with insecticidal soap...it is going to kill them.....so it is up to the user to watch that they don't hit other beneficial insects while spraying......both straight insecticidal soaps and ones with pyrethins are contact sprays....not residual like sevin etc......both break down very quickly......and don't kill bees etc after the fact.....
With that being said, I generally pick off sawfly larva, caterpillars etc from my shrubs and roses.....but on trees where it is hard to reach and there are dozens of these chewing creatures, then I recommend spraying......if it is older sawfly larva, you need something stronger than insecticidal soap.......found this out the hard way and after reviewing the literature, found that a pyrethin additive was needed.....
Cheers
Ian

kas4, if I spray a contact only insecticide (pyrethrum,say) against sawflies, say, how can I be sure to avoid beneficial insects? An old maxim is applicable.
Use the most benign product at its lowest effective dose.

I had an infestation of dogwood sawfly last year on a number of shrubs and trees and rid the plants and myself of them by hand picking and throwing them into soapy water.

Thanks for all of the great responses. So far I've been controlling these by removing them manually. However, they've gotten to the upper branches which I cannot reach even with my pole lopper fully extended and standing on a step ladder. The tree is about 30' high. My sprayer won't reach that height either. Any suggestions?